In many prior art systems utilizing cathode ray tubes, the brightness of the display on the CRT is controlled by a variable resistor such as a potentiometer with, for example, a wiper arm moving on a coil. However, there are some applications such as an airborne navigation computers where panel space for the system using the CRT is at a premium and there is very little room for the physical components required for a resistance which is varied mechanically. In addition, there are certain applications where it would be useful to have a computer be able to control the brightness of a CRT display directly without the need of a servomechanism or the like to operate a variable resistance.